If I wished to replace the webpagetest icon or include another one on my private instance of the application. Where would I find the files to do so, thanks.
Your best bet would be to override the css using the custom css support (custom.css in the settings directory). That way you don’t have to worry about overwriting files.
Otherwise, if you just want to modify the logo it is images/logo_private.png
I tried to change the logo_private.png icon to another simply by renaming it and now my server is giving a 500 error, thanks.